Microphone waterproofing device



June 12, 1951 w, CRAGG ETAL 2,556,168

MICROPHONE WATERPROOFING DEVICE Filed Sept. 27, 1947 INVENTORS WILL/AM 0. CAAGG MICHAEL L. HAYFORD BY Z ATTORNEY Patented June 1 2, 1951 MICROPHONE WATERPROOFING DEVICE William Donald Cragg and Michael Lawrence Gayford, London, England, assignors to International Standard York, N. Y.

Electric Corporation, New

Application September 27, 1947, Serial No. 776,568 In Great Britain October 2, 1946 6 Claims.

. H 1 This invention relates to the microphones such as are used for radio broadcasting and public address purposes and that has for its object the provision of unproved waterproofing for microphones intended for outdoor use.

The main feature of the invention comprises a waterproofing device for a microphone comprising a waterproof screen of material which does not substantially attenuate sound waves and means for preventing direct access of rain to the screen.

The invention will be clearly understood from the following description of a preferred embodiment illustrated in the accompanying drawings in which Fig. 1 is a cross sectional elevation of a microphone provided with a waterproof screen in accordance with the invention; while Fig. 2 is a side view partly in cross section of a windshield of the type described in our copending application No. 776,567, filed September 27, 1947 and which may be attached over the Waterproof screen.

The casing I of the microphone comprises a perforated dome 4 in front of the diaphragm 3 of the electromagnetic unit 2. A dust excluding screen 5 of fine mesh silk, about 100 filaments to the inch is usually attached to the dome 4.

The waterproof unit consists of a series of screens 6, l and B, spaced by washers 9 and fixed to the front of casing I by a clamping ring ID.

The first screen 6 is of closely woven umbrella silk. The second screen I is of perforated steel and is provided as mechanical protection for the silk screen 6. The third screen 8 is of stainless steel or silk mesh the filaments of which in accordance with our application Serial No. 776,567 are about 50 to the inch.

The basis of design is to provide a waterproof screen which does not substantially attenuate sound waves in the range 50-l0,000 C. P. S., and which is itself screened from direct impact of rain. The reason for this is that water on closely woven material with more than about 80 filaments to the inch, will form by surface tension a continuous film over the wetted part, and if the whole surface is wetted it will be completely covered with an unbroken film of water which will seriously attenuate sound above about 3,000 O. P. S. Partial wetting of the surface will not, however, have an appreciable attenuating effect.

The outer screen will have a mesh of less than 80 to the inch, preferably about 50 to the inch. The front screen 8 acts as a windshield without attenuating the sound waves, as described its whole surface.

in our above copending application. The filaments of the screen 8 are individually coated with oil, or with one of the silicone varnishes. The individual coating of the filaments rather than the formation of aifilm in the interstices of the filaments can be obtained in the case of oilfby application by means of an oil-carrying absorbent pad, and in the case of silicone varnish bysprayins.

The outer screen 8 acts as a windshield and also acts as a rainbreak, while the screen 6 prevents all access of moisture to the microphone. Rain on the screen 8 will not form a continuous film, while insufficient moisture will reach the screen 6 to form a continuous water film over It may be desired to apply more effective wind shielding to a microphone waterproofed'in the manner shown in Fig. 1. For this purpose a windshield of the type described in the above copending application may be. attached to the microphone over the waterproof attachment.

This is shown in Fig. 2 in which the Windshield comprises a spring clamp ring ll adapted to grip the ring l0 and carrying a substantially hemispherical woven screen l2 supported by a roughly hemispherical block I3 of fine filaments, the material and the gauge and spacing of the screen and block being such that they share substantially equally in the shielding effect.

Preferably the screen I! is woven from silk or stainless steel thread having a diameter of not substantially more than .0075 inch, which may if desired be reduced to about .0055 inch. The filaments are spaced about 50 threads to the inch.

Closer spacing up to to the inch may be used but the risk is run of getting a film of water over the whole screen in wet weather, with consequent serious attenuation of the sound waves. The block [3 is preferably of rubberised hair with an approximate density of 500 filaments to the square inch. Rubberised hair consists of horse hair or the like each with a thin coating of rubher which sticks the hairs together at spaced positions.

The wind-shield and microphone together have a substantially spherical form without sharp discontinuities. With this shield, the level of noise caused by winds in the range 10 to 30 M. P. H. is reduced between 12 and 16 db. whilst the attenuation of sound waves in the range 50 to 10,000

C. P. S. is negligible, except at the extreme high frequencies where there may be an attenuation of about 5 db.

Wei-claim:

1. A waterproofing device for a microphone comprising an assembly of perforate screens, means for supporting said screens in spaced parallel relation to one another and means for mounting said assembly in front of a microphone, the outermost of said screens comprising a woven screen of waterproof material, the filaments of said screen being of a diameter of less than .0075

inch, and being spaced in the order of fifty. to the inch.

2. Device according to claim 1 wherein'the filaments have individual protective coatings.

3. Device according to claim 2 wherein said protective coating comprises a silicone varnish.

4. Device according to claim 2 wherein said protective coating comprises an oil.

5. A waterproofing device according to claim 1, wherein the inner of said screens comprises a closely woven fabric material.

6. A waterproofing screenaccording to claim 5, further comprising a perforate metal screen in spaced relation between said inner and. outer screens.

WILLIAMDONALD .CRAGG.

MICHAEL LAWRENCE GAYFORD:

- 4 REFERENCES CITED The following references are of record in the V file of this'patent:

UNITED STATES PATENTS Number Name Date 1,901,065 Spotts Mar. 14, 1933 2,200,097 Phelps May 7, 1940 2,325,424 Rettinger July 27, 1943 2,346,226 Marlow Apr. 11, 1944 2,346,394 Rettinger Apr. 11, 1944 2,433,250 Weibler Dec. 23, 1947 FOREIGN PATENTS Number Country Date 425,186 Great Britain Mar. 8, 1935 425,558 Great Britain Mar. 18, 1935 7 OTHER REFERENCES Recording Sound for Motion Pictures, 1st

edition, McGraw-Hill, pages 124-125. (Copy :in Div. 16.) 

